Manufacture of viscose rayon



June 12, 1962 B. H. DAIMLER ETAL 3,038,778

MANUFACTURE OF VISCOSE RAYON Filed June 6, 1958 VISCOSE SPINNING SOLUTION EX TRUSION COAGULATING AND REGENERATING BATH AQUEOUS INTERMEDIATE BATH HOT STRETCH BATH INVENTORS alkrnano Q'mI- W060 ILL/Ara- AMP Run-unto 51-83.

BYZIMZZ ATTORNEY United States i atent i 3,033,778 MANUFACTURE (PF VISCQSE RAYON Berthold H. Daimler, Heinsberg, Hugo Eiling, Oberhruch- Grebben, and Richard Elssner, Randerath, Germany,

assignors to American Erika Corporation, Erika, N.C.,

a corporation of Delaware Filed .lunc 6, 1958, Eier. No. 740,189 Claims priority, application Germany June 21, 1957 6 Claims. (CI. 13-54) The present invention relates to the manufacture of viscose rayon and more particularly to a process for producing high strength viscose rayon wherein the stretch tension of freshly spun viscose rayon threads is lowered and the stretchability of such threads is increased.

In the production of viscose rayon threads viscose solution is extruded through a spinneret into a coagulating and regenerating bath comprising an aqueous acid solution and containing sulfate salts. In order to obtain threads having high strength, it is necessary to subject the freshly spun threads to strong stretching after coagulation but before complete regeneration thereof. Generally, the strength increases in direct proportion to the increase in stretch. The conventional system used to impart a strong stretch to freshly spun threads is known as the two-bat spinning process which includes the aforesaid coagulating and regenerating bath and a second stretch bath that is maintained at a high temperature, for example, in the range from 50 to 90 C. At this temperature the threads during their passage through the second bath are capable of accepting a high degree of stretch Without rupture. The second bath usually is composed of a dilute acid solution but may be alkaline, in which case the alkaline bath may also contain compounds of zinc or aluminum.

Obviously, the stretch is limited to a fixed value for a given set of spinning conditions and cannot exceed the breaking point of the thread. When stretching exceeds this point, the broken threads cause entanglement and the threads so produced have an undesirable fibrous character. Consequently, it would be advantageous to increase the stretchability of freshly spun viscose threads without causing thread breakage. 7 An increase in such stretchability would be indicated either by being able to stretch eyond the normal breaking point of the threads or by achieving a lowering of the tension necessary to impart a given stretch to the threads.

It is an object of this invention to provide a process for effectively producing regenerated cellulose threads from viscose having improved physical properties.

Another object is to provide an improved process in which the stretchability of freshly spun regenerated cellulose threads from viscose is increased.

A further object is to provide an improved process in which freshly spun regenerated cellulose threads from viscose exhibit an increased stretchability in a hot second stretch bath.

These and other objects are accomplished by extruding a viscose solution through a spinneret into a coagulating and regenerating first bath containing an acid and salts to form viscose threads, withdrawing the thus-formed threads from the bath, passing the threads through a cold aqueous intermediate bath maintained at a temperature of from 15 to 35 C. after withdrawal of the threads from the first bath, and thereafter subjecting the threads to an appreciable stretch in a hot, dilutely acidic second bath. The threads may be stretched to a greater extent in the second bath than threads produced under like conditions but not subjected to the cold intermediate bath treatment.

The increased stretchability obtainable was quite unobvions and unpredictable since heretofore it Was thought that passing the threads from the spinbath directly into a .3,@38,773 Patented June 12, 1952 ice hot second stretch bath Where the threads are heated was necessary in order to impart additional plasticity to the threads. Moreover, cooling of the freshly spun threads is ordinarily regarded as undesirable because when the threads are cooled, they lose their plasticity. The reason that one is able to obtain the marked improvement in the stretchability of the threads by a brief lowering of the temperature of the threads is not clearly understood. On the other hand, the action of the ordinary Ihot stretch second bath in regard to increasing the stretchability of the threads also cannot be fully explained.

it was found that the effect of the cold aqueous intermediate bath increases with the proportion of the salts entrained in the threads from the first bath which are washed out by conducting the threads through the intermediate bath. Such salts include sodium sulfate and zinc sulfate.

In producing threads by means of the process of the present invention, a notable and further improvement in the strength value of the threads is obtained by maintaining the acid concentration in the cold intermediate bath within the range of 10 to 40 grams of acid per kilogram of the bath. It is highly important to avoid the use of a high acid concentration in the intermediate bath, because at high acid concentrations, any lowering of tension induced by the washing of the thread would be cancelled. The preferred acid concentration depends on the spinning conditions with optimum results being obtained when the liquid in the threads after leaving the intermediate bath but before same enters the hot second bath has an acid content of 2 to 30 grams per kilogram, preferably 5 to 20 grams per kilogram.

It is essential that the temperature of the intermediate bath be below 40 0., because above this temperature stretchability of the threads is reduced. The reduced stretchability may be attributed to the fact that at temperatures above 40 C. the regeneration of the cellulose is accelerated. The minimum temperature necessary to obtain the enhanced stretchability of the present invention is about 15 C. below this temperature one does not attain any additional substantial increase in stretchability. The preferred temperature range is between 20 and 30 C.

Further, it was found that small quantities of formaldehyde when added to the cold intermediate bath increase once more the extent to which the threads may be stretched without filamentary breakage. Preferably 0.5 to 10 grams of formaldehyde are added to each kilogram of bath. The treatment of threads with aldehyde in an intermediate bath before the threads are stretched in a hot second bath has been described in U.S. Patent No. 2,452,130. Because of the combined effect of the threadwashing in the cold intermediate bath of the present invention and the effect of the formaldehyde, improved stretchability comparable to that of the patent is achieved with the use of considerably less formaldehyde.

The invention is illustrated by the following examples wherein percentages are given by Weight unless otherwise indicated.

EXAMPLE I A viscose solution having the composition of 7.2% cellulose and 5.4% alkali and a xanthate ratio of 46 was extruded through a spin-neret having 1000 orifices into an aqueous coagulating and regenerating spinbath. To each kilogram. of the viscose solution, 1.7 grams of the ethoxylated aliphatic amine having the general formula:

wherein x-l-y has a mean value of 20, had been incorporated. The spinbath contained 40 grams of H per kilogram of bath, 120 grams of Na SO per kilogram of bath, and 50 grams of ZnSO per kilogram of bath, and had a temperature of 40 C. The length of thread immersion in the spinbath was 70 cm. The threads were withdrawn from the bath and passed through a cold intermediate bath for a distance of 25 cm. For this purpose, a deflecting roller associated with a first withdrawal system and which ran in a tray through which the intermediate bath flowed was used. The temperature of the intermediate bath was 25 C. After the threads were withdrawn from the intermediate bath, they were stretched 100% in a conventional hot second stretch bath.

The following table represents the observations of a series of experiments where difierent intermediate bath compositions were used. The stretch tension listed therein was measured as the threads were being withdrawn from the second bath. A control test in which no cold intermediate bath was employed is given for comparative purposes.

From this data, it is seen that the threads which were spun without being conducted through an intermediate bath required the highest tension in order to be stretched 100% in the 'hot second bath. The threads which were conducted through an intermediate bath required much less tension to be stretched the same amount. The data in the above table show that the tension gradually increased as the concentration of H SO in the intermediate bath was increased.

In order to maintain the preferred minimum concentration of H 80 in the spinning thread as previously discussed, it was suflicient under the present spinning conditions to use an acid concentration in the intermediate bath of -20 g./l. It can be noted from the data in the above table that under these conditions a lowering of the stretch tension of approximately 30% was achieved.

EXAMPLE II A viscose solution having the composition of 6.1% cellulose and 4.2% alkali and a xanthate ratio of 43 was extruded through a spinneret having 1000 orifices into an aqueous coagulating and regenerating spinbath. Each kilogram of the viscose solution contained 0.2 gram of the amine described in Example I. The spinbath contained 30 grams of H 50 per kilogram of bath, 200 grams of Na SO per kilogram of bath, and 70 grams of ZnSO per kilogram of bath, and had a temperature of 55 C. The length of thread immersion in the spinbath was 35 cm.

In one spinning experiment, the threads were withdrawn from the spinbath and passed directly in a hot second stretch bath where the threads were stretched 85%. The thread immersion in the second bath was 180 cm. The stretch tension required to impart such stretch was 1500 grams.

In a second spinning experiment, the threads before being stretched 85% in the hot second bath as above were passed through an aqueous intermediate bath hav ing a temperature of C. and containing 15 grams of H 80 per kilogram of bath. The stretch tension required in this instance to impart a stretch of 85% was only 1280 grams. Therefore, the stretch tension was lowered 15% by the employment of the cold intermediate bath.

4 EXAMPLE III A viscose solution having the composition of 6.5% cellulose and 5.5% alkali and containing 1.7 grams of the amine described in Example I per kilogram of solution was extruded through a spinneret having 720 orifices with an orifice diameter of 60 m into an aqueous coagulating and regenerating spinbath. The spinbath contained 50 grams of H SO per kilogram of bath, 130 grams of Na SO per kilogram of bath, and 60 grams of ZnSO per kilogram of bath, and had a temperature of 48 C. Spinnings were conducted without an intermediate bath and also with an intermediate bath containing 25 grams of H per kilogram of bath. A third spinning was conducted in which 4 grams of formaldehyde per kilogram of bath had been added to the intermediate bath. The intermediate bath was contained in a small trough and was constantly supplied thereto from a larger storage container, with the bath being discharged and returned to the container. In order to keep the concentration of the acid and formaldehyde within acceptable limits upon extended spinning, it was necessary to reject a certain quantity of the used bath continuously and replace it with fresh bath.

Drawing in the hot second stretch bath was so adjusted that a tension of approximately 1200 g. existed in each of these spinnings. The data in Table II below show that with employment of the intermediate bath the threads can be stretched to a greater extent than Without the bath. Further, the elongation of the threads both in the wet and dry conditions are lowered when the intermediate bath was used. It is noteworthy that the elongation of a cord formed in the usual manner is also reduced as the result of the increased stretch. In the data given in connection with the threads in a wet condition, it is to be noted that the threads had been given a slashing stretch of 11% and then dried.

Table II Composition of intermediate bath:

Since many variations of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the above specific illustrations except to the extent of the following claims.

What is claimed is:

1. A process for producing high strength viscose threads comprising extruding a viscose solution into an aqueous acidic coagulating and regenerating first bath containing salts to form viscose threads therefrom, withdrawing the thus-formed threads from said first bath, passing said threads through a cold aqueous intermediate bath maintained at a temperature of 1535 C. but substantially lower than the temperature of said first bath, whereby the salt content of the liquid entrained in said threads is reduced by their contact with said intermediate bath, and passing said threads into a hot second bath maintained at a temperature substantially higher than the temperature of said first bath wherein said threads are given a substantial stretch.

2. A process for producing high strength viscose threads comprising extruding a viscose solution into an aqueous acidic coagulating and regenerating first bath containing salts to form viscose threads therefrom, withdrawing the thus-formed threads from said first bath, passing said threads through a cold aqueous intermediate bath containing a small amount of sulfuric acid and maintained at a temperature of 15-35 C. but substantially lower than the temperature of said first bath, whereby the salt content of the liquid entrained in said threads is reduced by their contact with said intermediate bath, and passing said threads into a hot second bath maintained at a temperature substantially higher than the temperature of said first bath wherein said threads are given a substantial stretch.

3. A process for producing high strength viscose threads comprising extruding a viscose solution into an aqueous acidic coagulating and regenerating first bath containing salts to form viscose threads therefrom, withdrawing the thus-formed threads from said first bath, passing said threads through a cold aqueous intermediate bath containing -40 grams of sulfuric acid per kilogram of intermediate bath and maintained at a temperature of -35 C. but substantially lower than the temperature of said first bath, whereby the salt content of the liquid entrained in said threads is reduced by their contact with said intermediate bath, and passing said threads into a hot second bath maintained at a temperature substantially higher than the temperature of said first bath wherein said threads are given a substantial stretch.

4. A process for producing high strength viscose threads comprising extruding a viscose solution into an aqueous acidic coagulating and regenerating first bath containing salts to form viscose threads therefrom, withdrawing the thus-formed threads from said first bath, passing said threads through a cold aqueous intermediate bath containing 10-40 grams of sulfuric acid per kilogram of intermediate bath and maintained at a temperature of -30 C. but substantially lower than the temperature of said first bath, whereby the salt content of the liquid entrained in said threads is reduced by their contact with said intermediate bath, and passing said threads into a hot second bath maintained at a tempera ture substantially higher than the temperature of said first bath wherein said threads are given a substantial stretch.

5. A process to; producing high strength viscose threads comprising extruding a viscose solution into an aqueous acidic coagulating and regenerating first bath containing salts to form viscose threads therefrom, withdrawing the thus-formed threads from said first bath, passing said threads through a cold aqueous intermediate bath containing 10-40 grams of sulfuric acid per kilogram of intermediate bath and formaldehyde and maintained at a temperature of 15-35 C. but substantially lower than the temperature of said first bath, whereby the salt content of the liquid entrained in said threads is reduced by their contact with said intermediate bath, and passing said threads into a hot second bath maintained at a temperature substantially higher than the temperature of said first bath wherein said threads are given a substantial stretch.

6. A process for producing high strength viscose threads comprising extruding a viscose solution into an aqueous coagulating and regenerating first bath containing sulfuric acid, sodium sulfate and zinc sulfate to form viscose threads therefrom, withdrawing the thus-formed threads from said first bath, passing said threads through a cold aqueous intermediate bath containing 10-40 grams of sulfuric acid per kilogram of intermediate bath and maintained at a temperature of 20-30" C. but substantially lower than the temperature of said first bath, whereby the salt content of the liquid entrained in said threads is reduced by their contact with said intermediate bath, and passing said threads into a hot second bath maintained at a temperature substantially higher than the temperature of said first bath wherein said threads are given a substantial stretch.

References Cited in the file of this patent UNITED STATES PATENTS 2,192,074 Givens Feb. 27, 1940 2,297,613 Fink et al. Sept. 29, 1942 2,327,516 Fink et al. Aug. 24, 1943 2,452,130 Kayser Oct. 26, 1948 2,882,122 Emery Apr. 14, 1959 FOREIGN PATENTS 166,305 Australia Dec. 12, 1955 

1. A PROCESS FOR PRODUCING HIGH STRENGTH VISCOSE THREADS COMPRISING EXTRUDING A VISCOSE SOLUTION INTO AN AQUEOUS ACIDIC COAGULATING AND REGENERATING FIRST BATH CONTAINING SALTS TO FORM VISCOSE THREADS THEREFROM, WITHDRAWING THE THUS-FORMED THREADS FROM SAID FIRST BATH, PASSING SAID THREADS THROUGH A COLD AQUEOUS INTERMEDIATE BATH MAINTAINED AT A TEMPERATURE OF 15-35* C. BUT SUBSTANTIALLY LOWER THAN THE TEMPERATURE OF SAID FIRST BATH, WHEREBY THE SALT CONTENT OF THE LIQUID ENTRAINED IN SAID THREADS IS REDUCED BY THEIR CONTACT WITH SAID INTERMEDIATE BATH, AND PASSING SAID THREADS INTO A HOT SECOND BATH MAINTAINED AT A TEMPERATURE SUBSTANTIALLY HIGHER THAN THE TEMPERATURE OF SAID FIRST BATH WHEREIN SAID THREADS ARE GIVEN A SUBSTANTIALLY STRETCH. 